Nozzle guard for a printhead

ABSTRACT

An ink jet printhead has a number of printhead chips. Each printhead chip has a wafer substrate. A plurality of nozzle arrangements is positioned on the wafer substrate. Each nozzle arrangement has nozzle chamber walls and a roof wall that define a nozzle chamber and a nozzle opening in fluid communication with the nozzle chamber. An actuator is operatively arranged with respect to each nozzle arrangement to eject ink from the nozzle chamber through the nozzle opening. A nozzle guard is positioned over the printhead chip. The nozzle guard has a support structure and a planar cover member. The planar cover member is positioned on the support structure. The planar cover member defines a plurality of passages. Each passage is in register with a respective nozzle opening. The planar cover member is less than 300 microns thick.

REFERENCES TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part application of U.S.application Ser. No. 09/575,125. Various methods, systems and apparatusrelating to the present invention are disclosed in the followingco-pending applications filed by the applicant or assignee of thepresent invention simultaneously with the present application:09/575,197 09/575,195 09/575,159 09/575,132 09/575,123 09/575,14809/575,130 09/575,165 09/575,153 09/575,118 09/575,131 09/575,11609/575,144 09/575,139 09/575,186 09/575,185 09/575,191 09/575,14509/575,192 09/575,181 09/575,193  9/575,156 09/575,183 09/575,16009/575,150 09/575,169 09/575,184 09/575,128 09/575,180 09/575,14909/575,179 09/575,133 09/575,143 09/575,187 09/575,155 09/575,19609/575,198 09/575,178 09/575,164 09/575,146 09/575,174 09/575,16309/575,168 09/575,154 09/575,129 09/575,124 09/575,188 09/575,18909/575,162 09/575,172 09/575,170 09/575,171 09/575,161 09/575,14109/575,125 09/575,142 09/575,140 09/575,190 09/575,138 09/575,12609/575,127 09/575,158 09/575,117 09/575,147 09/575,152 09/575,17609/575,151 09/575,177 09/575,175 09/575,115 09/575,114 09/575,11309/575,112 09/575,111 09/575,108 09/575,109 09/575,182 09/575,17309/575,194 09/575,136 09/575,119 09/575,135 09/575,157 09/575,16609/575,134 09/575,121 09/575,137 09/575,167 09/575,120 09/575,122

[0002] These applications are incorporated by reference.

FIELD OF THE INVENTION

[0003] This invention relates to ink jet printheads. More particularly,the invention relates to an ink jet printhead having at least oneprinthead chip that includes a nozzle guard to protect the chip.

BACKGROUND TO THE INVENTION

[0004] As set out in the material incorporated by reference, theApplicant has developed ink jet printheads that can span a print mediumand incorporate up to 84 000 nozzle assemblies.

[0005] These printheads includes a number of printhead chips. Theprinthead chips include micro-electromechanical components whichphysically act on ink to eject ink from the printhead chips. Suchcomponents are delicate and require careful handling to avoid damage.

[0006] Applicant has conceived a means for protecting such chips.

SUMMARY OF THE INVENTION

[0007] According to the invention there is provided an ink jet printheadwhich comprises

[0008] at least one printhead chip that comprises

[0009] a wafer substrate;

[0010] a plurality of nozzle arrangements positioned on the wafersubstrate, each nozzle arrangement having nozzle chamber walls and aroof wall that define a nozzle chamber and a nozzle opening in fluidcommunication with said nozzle chamber; and

[0011] an actuator that is operatively arranged with respect to eachnozzle arrangement to eject ink from said nozzle chamber through thenozzle opening on demand; and

[0012] a nozzle guard positioned over the printhead chip, the nozzleguard comprising

[0013] a support structure that extends from the printhead chip; and

[0014] a planar cover member positioned on the support structure, theplanar cover member defining a plurality of passages, each passage beingin register with a respective nozzle opening, the planar cover memberbeing less than approximately 300 microns thick.

[0015] The support structure of the nozzle guard may define a number ofopenings that permit the ingress of air into a region between theprinthead chip and the cover member, so that the air can pass throughthe passages.

[0016] The cover member and the support structure may be defined by awafer substrate.

[0017] In this specification, the term “nozzle” is to be understood asan element defining an opening and not the opening itself.

[0018] The nozzle may comprise a crown portion, defining the opening,and a skirt portion depending from the crown portion, the skirt portionforming a first part of a peripheral wall of the nozzle chamber.

[0019] The printhead may include an ink inlet aperture defined in afloor of the nozzle chamber, a bounding wall surrounding the apertureand defining a second part of the peripheral wall of the nozzle chamber.It will be appreciated that said skirt portion is displaceable relativeto the substrate and, more particularly, towards and away from thesubstrate to effect ink ejection and nozzle chamber refill,respectively. Said bounding wall may then serve as an inhibiting meansfor inhibiting leakage of ink from the chamber. Preferably, the boundingwall has an inwardly directed lip portion or wiper portion which servesa sealing purpose, due to the viscosity of the ink and the spacingbetween said lip portion and the skirt portion, for inhibiting inkejection when the nozzle is displaced towards the substrate.

[0020] Preferably, the actuator is a thermal bend actuator. Two beamsmay constitute the thermal bend actuator, one being an active beam andthe other being a passive beam. By “active beam” is meant that a currentis caused to flow through the active beam upon activation of theactuator whereas there is no current flow through the passive beam. Itwill be appreciated that, due to the construction of the actuator, whena current flows through the active beam it is caused to expand due toresistive heating. Due to the fact that the passive beam is constrained,a bending motion is imparted to the connecting member for effectingdisplacement of the nozzle.

[0021] The beams may be anchored at one end to an anchor mounted on, andextending upwardly from, the substrate and connected at their opposedends to the connecting member. The connecting member may comprise an armhaving a first end connected to the actuator with the nozzle connectedto an opposed end of the arm in a cantilevered manner. Thus, a bendingmoment at said first end of the arm is exaggerated at said opposed endto effect the required displacement of the nozzle.

[0022] The printhead may include a plurality of nozzles each with theirassociated actuators and connecting members, arranged on the substrate.Each nozzle, with its associated actuator and connecting member, mayconstitute a nozzle assembly.

[0023] The printhead may be formed by planar monolithic deposition,lithographic and etching processes and, more particularly, the nozzleassemblies may be formed on the printhead by these processes.

[0024] The substrate may include an integrated drive circuit layer. Theintegrated drive circuit layer may be formed using a CMOS fabricationprocess.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The invention is now described, by way of example, with referenceto the accompanying diagrammatic drawings in which:

[0026]FIG. 1 shows a three dimensional, schematic view of a nozzleassembly of a printhead chip for an ink jet printhead in accordance withthe invention;

[0027] FIGS. 2 to 4 show a three dimensional, schematic illustration ofan operation of the nozzle assembly of FIG. 1;

[0028]FIG. 5 shows a three-dimensional view of an array of the nozzleassemblies of FIGS. 1 to 4 constituting the printhead chip;

[0029]FIG. 6 shows, on an enlarged scale, part of the array of FIG. 5;

[0030]FIG. 7 shows a three dimensional view of the ink jet printheadchip with a nozzle guard positioned over the printhead chip;

[0031]FIGS. 8a to 8 r show three-dimensional views of steps in themanufacture of a nozzle assembly of an ink jet printhead;

[0032]FIGS. 9a to 9 r show sectional side views of the manufacturingsteps;

[0033]FIGS. 10a to 10 k show layouts of masks used in various steps inthe manufacturing process;

[0034]FIGS. 11a to 11 c show three-dimensional views of an operation ofthe nozzle assembly manufactured according to the method of FIGS. 8 and9; and

[0035]FIGS. 12a to 12 c show sectional side views of an operation of thenozzle assembly manufactured according to the method of FIGS. 8 and 9.

DETAILED DESCRIPTION OF THE DRAWINGS

[0036] In FIG. 1 of the drawings, reference 10 indicates a nozzleassembly of a printhead chip of a printhead, in accordance with theinvention, is designated generally by the reference numeral 10. Theprinthead has a plurality of printhead chips 10 arranged in an array 14(FIGS. 5 and 6) on a silicon substrate 16. The array 14 will bedescribed in greater detail below.

[0037] The nozzle assembly 10 includes a silicon substrate or wafer 16on which a dielectric layer 18 is deposited. A CMOS passivation layer 20is deposited on the dielectric layer 18.

[0038] Each nozzle assembly 10 includes a nozzle 22 defining a nozzleopening 24, a connecting member in the form of a lever arm 26 and anactuator 28. The lever arm 26 connects the actuator 28 to the nozzle 22.

[0039] As shown in greater detail in FIGS. 2 to 4 of the drawings, thenozzle 22 comprises a crown portion 30 with a skirt portion 32 dependingfrom the crown portion 30. The skirt portion 32 forms part of aperipheral wall of a nozzle chamber 34 (FIGS. 2 to 4 of the drawings).The nozzle opening 24 is in fluid communication with the nozzle chamber34. It is to be noted that the nozzle opening 24 is surrounded by araised rim 36 which “pins” a meniscus 38 (FIG. 2) of a body of ink 40 inthe nozzle chamber 34.

[0040] An ink inlet aperture 42 (shown most clearly in FIG. 6 of thedrawings) is defined in a floor 46 of the nozzle chamber 34. Theaperture 42 is in fluid communication with an ink inlet channel 48defined through the substrate 16.

[0041] A wall portion 50 bounds the aperture 42 and extends upwardlyfrom the floor portion 46. The skirt portion 32, as indicated above, ofthe nozzle 22 defines a first part of a peripheral wall of the nozzlechamber 34 and the wall portion 50 defines a second part of theperipheral wall of the nozzle chamber 34.

[0042] The wall 50 has an inwardly directed lip 52 at its free end whichserves as a fluidic seal which inhibits the escape of ink when thenozzle 22 is displaced, as will be described in greater detail below. Itwill be appreciated that, due to the viscosity of the ink 40 and thesmall dimensions of the spacing between the lip 52 and the skirt portion32, the inwardly directed lip 52 and surface tension function as a sealfor inhibiting the escape of ink from the nozzle chamber 34.

[0043] The actuator 28 is a thermal bend actuator and is connected to ananchor 54 extending upwardly from the substrate 16 or, moreparticularly, from the CMOS passivation layer 20. The anchor 54 ismounted on conductive pads 56 which form an electrical connection withthe actuator 28.

[0044] The actuator 28 comprises a first, active beam 58 arranged abovea second, passive beam 60. In a preferred embodiment, both beams 58 and60 are of, or include, a conductive ceramic material such as titaniumnitride (TiN).

[0045] Both beams 58 and 60 have their first ends anchored to the anchor54 and their opposed ends connected to the arm 26. When a current iscaused to flow through the active beam 58 thermal expansion of the beam58 results. As the passive beam 60, through which there is no currentflow, does not expand at the same rate, a bending moment is createdcausing the arm 26 and thus the nozzle 22 to be displaced downwardlytowards the substrate 16 as shown in FIG. 3 of the drawings. This causesan ejection of ink through the nozzle opening 24 as shown at 62 in FIG.3 of the drawings. When the source of heat is removed from the activebeam 58, i.e. by stopping current flow, the nozzle 22 returns to itsquiescent position as shown in FIG. 4 of the drawings. When the nozzle22 returns to its quiescent position, an ink droplet 64 is formed as aresult of the breaking of an ink droplet neck as illustrated at 66 inFIG. 4 of the drawings. The ink droplet 64 then travels on to the printmedia such as a sheet of paper. As a result of the formation of the inkdroplet 64, a “negative” meniscus is formed as shown at 68 in FIG. 4 ofthe drawings. This “negative” meniscus 68 results in an inflow of ink 40into the nozzle chamber 34 such that a new meniscus 38 (FIG. 2) isformed in readiness for the next ink drop ejection from the nozzleassembly 10.

[0046] Referring now to FIGS. 5 and 6 of the drawings, the nozzle array14 is described in greater detail. The array 14 is for a four-colorprinthead. Accordingly, the array 14 includes four groups 70 of nozzleassemblies, one for each color. Each group 70 has its nozzle assemblies10 arranged in two rows 72 and 74. One of the groups 70 is shown ingreater detail in FIG. 6 of the drawings.

[0047] To facilitate close packing of the nozzle assemblies 10 in therows 72 and 74, the nozzle assemblies 10 in the row 74 are offset orstaggered with respect to the nozzle assemblies 10 in the row 72. Also,the nozzle assemblies 10 in the row 72 are spaced apart sufficiently farfrom each other to enable the lever arms 26 of the nozzle assemblies 10in the row 74 to pass between adjacent nozzles 22 of the assemblies 10in the row 72. It is to be noted that each nozzle assembly 10 issubstantially dumbbell shaped so that the nozzles 22 in the row 72 nestbetween the nozzles 22 and the actuators 28 of adjacent nozzleassemblies 10 in the row 74.

[0048] Further, to facilitate close packing of the nozzles 22 in therows 72 and 74, each nozzle 22 is substantially hexagonally shaped.

[0049] It will be appreciated by those skilled in the art that, when thenozzles 22 are displaced towards the substrate 16, in use, due to thenozzle opening 24 being at a slight angle with respect to the nozzlechamber 34, ink is ejected slightly off the perpendicular. It is anadvantage of the arrangement shown in FIGS. 5 and 6 of the drawings thatthe actuators 28 of the nozzle assemblies 10 in the rows 72 and 74extend in the same direction to one side of the rows 72 and 74. Hence,the ink droplets ejected from the nozzles 22 in the row 72 and the inkdroplets ejected from the nozzles 22 in the row 74 are parallel to oneanother resulting in an improved print quality.

[0050] Also, as shown in FIG. 5 of the drawings, the substrate 16 hasbond pads 76 arranged thereon which provide the electrical connections,via the pads 56, to the actuators 28 of the nozzle assemblies 10. Theseelectrical connections are formed via the CMOS layer (not shown).

[0051] Referring to FIG. 7 of the drawings, a development of theinvention is shown. With reference to the previous drawings, likereference numerals refer to like parts, unless otherwise specified.

[0052] A nozzle guard 80 is mounted on the substrate 16 of the array 14.The nozzle guard 80 includes a planar cover member 82 having a pluralityof passages 84 defined therethrough. The passages 84 are in registerwith the nozzle openings 24 of the nozzle assemblies 10 of the array 14such that, when ink is ejected from any one of the nozzle openings 24,the ink passes through the associated passage 84 before striking theprint media.

[0053] The cover member 82 is mounted in spaced relationship relative tothe nozzle assemblies 10 by a support structure in the form of limbs orstruts 86. One of the struts 86 has air inlet openings 88 definedtherein.

[0054] The cover member 82 and the struts 86 are of a wafer substrate.Thus, the passages 84 are formed with a suitable etching process carriedout on the cover member 82. The cover member 82 has a thickness of notmore than approximately 300 microns. This speeds the etching process.Thus, the manufacturing cost is minimized by reducing etch time.

[0055] In use, when the array 14 is in operation, air is charged throughthe inlet openings 88 to be forced through the passages 84 together withink travelling through the passages 84.

[0056] The ink is not entrained in the air since the air is chargedthrough the passages 84 at a different velocity from that of the inkdroplets 64. For example, the ink droplets 64 are ejected from thenozzles 22 at a velocity of approximately 3 m/s. The air is chargedthrough the passages 84 at a velocity of approximately 1 m/s.

[0057] The purpose of the air is to maintain the passages 84 clear offoreign particles. A danger exists that these foreign particles, such asdust particles, could fall onto the nozzle assemblies 10 adverselyaffecting their operation. With the provision of the air inlet openings88 in the nozzle guard 80 this problem is, to a large extent, obviated.

[0058] Referring now to FIGS. 8 to 10 of the drawings, a process formanufacturing the nozzle assemblies 10 is described.

[0059] Starting with the silicon substrate or wafer 16, the dielectriclayer 18 is deposited on a surface of the wafer 16. The dielectric layer18 is in the form of approximately 1.5 microns of CVD oxide. Resist isspun on to the layer 18 and the layer 18 is exposed to mask 100 and issubsequently developed.

[0060] After being developed, the layer 18 is plasma etched down to thesilicon layer 16. The resist is then stripped and the layer 18 iscleaned. This step defines the ink inlet aperture 42.

[0061] In FIG. 8b of the drawings, approximately 0.8 microns of aluminum102 is deposited on the layer 18. Resist is spun on and the aluminum 102is exposed to mask 104 and developed. The aluminum 102 is plasma etcheddown to the oxide layer 18, the resist is stripped and the device iscleaned. This step provides the bond pads and interconnects to the inkjet actuator 28. This interconnect is to an NMOS drive transistor and apower plane with connections made in the CMOS layer (not shown).

[0062] Approximately 0.5 microns of PECVD nitride is deposited as theCMOS passivation layer 20. Resist is spun on and the layer 20 is exposedto mask 106 whereafter it is developed. After development, the nitrideis plasma etched down to the aluminum layer 102 and the silicon layer 16in the region of the inlet aperture 42. The resist is stripped and thedevice cleaned.

[0063] A layer 108 of a sacrificial material is spun on to the layer 20.The layer 108 is 6 microns of photo-sensitive polyimide or approximately4 μm of high temperature resist. The layer 108 is softbaked and is thenexposed to mask 110 whereafter it is developed. The layer 108 is thenhardbaked at 400° C. for one hour where the layer 108 is comprised ofpolyimide or at greater than 300° C. where the layer 108 is hightemperature resist. It is to be noted in the drawings that thepattern-dependent distortion of the polyimide layer 108 caused byshrinkage is taken into account in the design of the mask 110.

[0064] In the next step, shown in FIG. 8e of the drawings, a secondsacrificial layer 112 is applied. The layer 112 is either 2 μm ofphoto-sensitive polyimide which is spun on or approximately 1.3 μm ofhigh temperature resist. The layer 112 is softbaked and exposed to mask114. After exposure to the mask 114, the layer 112 is developed. In thecase of the layer 112 being polyimide, the layer 112 is hardbaked at400° C. for approximately one hour. Where the layer 112 is resist, it ishardbaked at greater than 300° C. for approximately one hour.

[0065] A 0.2 micron multi-layer metal layer 116 is then deposited. Partof this layer 116 forms the passive beam 60 of the actuator 28.

[0066] The layer 116 is formed by sputtering 1,000 Å of titanium nitride(TiN) at around 300° C. followed by sputtering 50 Å of tantalum nitride(TaN). A further 1,000 Å of TiN is sputtered on followed by 50 Å of TaNand a further 1,000 Å of TiN.

[0067] Other materials which can be used instead of TiN are TiB₂, MoSi₂or (Ti, Al)N.

[0068] The layer 116 is then exposed to mask 118, developed and plasmaetched down to the layer 112 whereafter resist, applied for the layer116, is wet stripped taking care not to remove the cured layers 108 or112.

[0069] A third sacrificial layer 120 is applied by spinning on 4 μm ofphotosensitive polyimide or approximately 2.6 μm high temperatureresist. The layer 120 is softbaked whereafter it is exposed to mask 122.The exposed layer is then developed followed by hardbaking. In the caseof polyimide, the layer 120 is hardbaked at 400° C. for approximatelyone hour or at greater than 300° C. where the layer 120 comprisesresist.

[0070] A second multi-layer metal layer 124 is applied to the layer 120.The constituents of the layer 124 are the same as the layer 116 and areapplied in the same manner. It will be appreciated that both layers 116and 124 are electrically conductive layers.

[0071] The layer 124 is exposed to mask 126 and is then developed. Thelayer 124 is plasma etched down to the polyimide or resist layer 120whereafter resist applied for the layer 124 is wet stripped taking carenot to remove the cured layers 108, 112 or 120. It will be noted thatthe remaining part of the layer 124 defines the active beam 58 of theactuator 28.

[0072] A fourth sacrificial layer 128 is applied by spinning on 4 μm ofphotosensitive polyimide or approximately 2.61 μm of high temperatureresist. The layer 128 is softbaked, exposed to the mask 130 and is thendeveloped to leave the island portions as shown in FIG. 9k of thedrawings. The remaining portions of the layer 128 are hardbaked at 400°C. for approximately one hour in the case of polyimide or at greaterthan 300° C. for resist.

[0073] As shown in FIG. 81 of the drawing a high Young's modulusdielectric layer 132 is deposited. The layer 132 is constituted byapproximately 1 μm of silicon nitride or aluminum oxide. The layer 132is deposited at a temperature below the hardbaked temperature of thesacrificial layers 108, 112, 120, 128. The primary characteristicsrequired for this dielectric layer 132 are a high elastic modulus,chemical inertness and good adhesion to TiN.

[0074] A fifth sacrificial layer 134 is applied by spinning on 2 μm ofphotosensitive polyimide or approximately 1.3 μm of high temperatureresist. The layer 134 is softbaked, exposed to mask 136 and developed.The remaining portion of the layer 134 is then hardbaked at 400° C. forone hour in the case of the polyimide or at greater than 300° C. for theresist.

[0075] The dielectric layer 132 is plasma etched down to the sacrificiallayer 128 taking care not to remove any of the sacrificial layer 134.

[0076] This step defines the nozzle opening 24, the lever arm 26 and theanchor 54 of the nozzle assembly 10.

[0077] A high Young's modulus dielectric layer 138 is deposited. Thislayer 138 is formed by depositing 0.2 μm of silicon nitride or aluminumnitride at a temperature below the hardbaked temperature of thesacrificial layers 108, 112, 120 and 128.

[0078] Then, as shown in FIG. 8p of the drawings, the layer 138 isanisotropically plasma etched to a depth of 0.35 microns. This etch isintended to clear the dielectric from all of the surface except the sidewalls of the dielectric layer 132 and the sacrificial layer 134. Thisstep creates the nozzle rim 36 around the nozzle opening 24 which “pins”the meniscus of ink, as described above.

[0079] An ultraviolet (UV) release tape 140 is applied. 4 μm of resistis spun on to a rear of the silicon wafer 16. The wafer 16 is exposed tomask 142 to back etch the wafer 16 to define the ink inlet channel 48.The resist is then stripped from the wafer 16.

[0080] A further UV release tape (not shown) is applied to a rear of thewafer 16 and the tape 140 is removed. The sacrificial layers 108, 112,120, 128 and 134 are stripped in oxygen plasma to provide the finalnozzle assembly 10 as shown in FIGS. 8r and 9 r of the drawings. Forease of reference, the reference numerals illustrated in these twodrawings are the same as those in FIG. 1 of the drawings to indicate therelevant parts of the nozzle assembly 10. FIGS. 11 and 12 show theoperation of the nozzle assembly 10, manufactured in accordance with theprocess described above with reference to FIGS. 8 and 9, and thesefigures correspond to FIGS. 2 to 4 of the drawings.

[0081] It will be appreciated by persons skilled in the art thatnumerous variations and/or modifications may be made to the invention asshown in the specific embodiments without departing from the spirit orscope of the invention as broadly described. The present embodimentsare, therefore, to be considered in all respects as illustrative and notrestrictive.

We claim:
 1. An ink jet printhead which comprises at least one printheadchip that comprises a wafer substrate; a plurality of nozzlearrangements positioned on the wafer substrate, each nozzle arrangementhaving nozzle chamber walls and a roof wall that define a nozzle chamberand a nozzle opening in fluid communication with said nozzle chamber;and an actuator that is operatively arranged with respect to each nozzlearrangement to eject ink from said nozzle chamber through the nozzleopening on demand; and a nozzle guard positioned over the printheadchip, the nozzle guard comprising a support structure that extends fromthe printhead chip; and a planar cover member positioned on the supportstructure, the planar cover member defining a plurality of passages,each passage being in register with a respective nozzle opening, theplanar cover member being less than approximately 300 microns thick. 2.An ink jet printhead as claimed in claim 1, in which the supportstructure of the nozzle guard defines a number of openings that permitthe ingress of air into a region between the printhead chip and thecover member, so that the air can pass through the passages.
 3. An inkjet printhead as claimed in claim 1, in which the support structure andthe cover member are defined by a wafer substrate.